1. Field of the Invention
The present invention relates generally to an optical cross-connect switching system applied to an optical transport network, and more particularly to a multi-dimensional optical cross-connect switching system that is capable of multi-dimensionally using wavelength resources, such as in the forms of optical fibers, optical wavelength bands and optical wavelengths.
2. Description of the Prior Art
An optical fiber telecommunication network can transmit a large amount of information at a high speed so that the network is highlighted as a method of dealing with rapidly increasing Internet traffic. For example, a transmission of several tens of Giga bits can be achieved by the optical fiber telecommunication network.
In this optical fiber telecommunication network, a wavelength division multiplexing (WDM) has been employed as a very effective method in transmitting a plurality of optical signals having different wavelengths via a single optical fiber, thereby effectively using the wide bandwidth provided by the optical fiber.
Generally, the optical fiber telecommunication network consists of switching systems for performing optical cross-connect switching at intermediate nodes and optical fibers for connecting the switching systems to one another. It is largely required that those switching systems should be provisioned with routing capability to local networks connected to intermediate nodes in the optical transport network, so switching systems capable of carrying out optical cross connect operations are employed as the switching systems. The present invention relates to these optical cross-connect switching systems.
Hereinafter, a conventional optical cross-connect switching system will be described with reference to the accompanying drawings.
In FIG. 1, a general optical cross-connect switching system is shown.
Referring to the FIG. 1, the general optical cross-connect switching system comprises an optical switch module 13 having a switching capacity of (Nm+k)×(Nm+k), N amplifiers 11-1 to 11-N connected to N input optical fibers, respectively, N demultiplexers 12-1 to 12-N connected to the N amplifiers 11-1 to 11-N and the optical switch module 13, respectively, N amplifiers 15-1 to 15-N connected to N output optical fibers, respectively, and N multiplexers 14-1 to 14-N connected to the N amplifiers 15-1 to 15-N and the optical switch module 13, respectively. A transmission unit 16 of a local network (not shown) is connected to the optical switch module 13 through k optical links, while a reception unit 17 of the local network is connected to the optical switch module 13 through k optical links.
In the general optical cross-connect switching system constructed as described above, signals multiplexed through the input optical fibers are transmitted. These signals are amplified by amplifiers, and then split into m wavelengths by the demultiplexers 12-1 to 12-N. Accordingly, a total of N×m wavelengths are inputted to the optical switch module 13. Meanwhile, in order to transmit signals from a local network to another optical cross-connect switching system in the optical transport network or from another optical cross-connect switching system to the local network, the local network is connected to the optical cross-connect switching system, to which the network belongs through the transmission unit 16 and the reception unit 17. In FIG. 1, k inserted wavelengths inputted through the transmission unit 16 of the local network are combined together and a total of Nm+k wavelengths are switched in the optical switch module 13. The switched signals are multiplexed by the m signals by the multiplexer 14-1 to 14-N, amplified by the amplifier 15-1 to 15-N, and then transmitted to the optical transport network through N output optical fibers. K inserted wavelengths of the switched signals are transmitted to the local network through the reception unit 17.
The general optical cross-connect switching system having such a structure can one-dimensionally use wavelength resources. When the number of inserted and extracted wavelengths, the numbers of the input/output optical fibers and the number of multiplexed wavelengths per optical link are changed, the system has the problem of being not able to adapt to the change without considerably changing its internal mechanical structure. Also the internal modification evoke concomitant changes in the neighbor nodes connected to the system through the network. That is, in the general optical cross-connect switching system, there is little scalability for the above-mentioned elements.
Next, with reference to FIG. 2, recently proposed an existing multi-granularity optical cross-connect switching system is described.
The multi-granularity optical cross-connect switching system shown in FIG. 2 was suggested to increase the capacity of an optical transport network while maintaining a complexity at an appropriate level. The switching system shown in FIG. 2 is disclosed in a thesis by Nairie and C. Blaizot entitled “Multi-Granularity Optical Cross connect” on ECOC200, Munich, page 269-270, September 2000.
Referring to FIG. 2, the multi-granularity optical cross-connect switching system consists of a Fiber Cross-Connect (FXC) switch 210, a Bandwidth Cross-Connect (BXC) switch 220, and a Wavelength Cross-Connect (WXC) switch 230.
The switches 210, 220 and 230 have space division switches 211, 221, 231 to perform cross-connect switching, respectively. Input optical fibers A and output fibers B are connected to only the FXC switch 210. The space division switch 211 performs cross-connect switching between the input optical fibers A and optical fibers from a local network or BXC switch 220, and the output optical fibers B and optical fibers toward the local network or BXC switch 220. Part of the input optical fibers is sent to a local network (not shown) as extraction fibers (extraction F), while part of the fibers is sent to the BXC switch 220.
In the BXC switch 220, the fiber-waveband conversion of inputted optical fibers is performed by demultiplexers 222 and 223. The converted wavebands are inputted to the space division switch 221. In the space division switch 221, part of the fibers is sent to the local network as an extraction band (extraction B) and part of the fibers is sent to the WXC switch 230. The space division switch 221 performs cross-connect switching between input wavebands and wavebands from the local network or WXC switch 230, and output wavebands and wavebands toward the local network or WXC switch 230. The output wavebands of the space division switch 221 undergo band-fiber conversion, and then are sent to the FXC switch 210.
In the WXC switch 230, the waveband-wavelength conversion of the wavebands from the BXC switch 220 is performed by the demultiplexers 232 and 233, and the obtained wavelengths are inputted to the space division switch 231. In addition, the space division switch 231 is provided with insertion wavelengths (insertion W) from the local network and provides extraction wavelengths (extraction W) to the local network. Output wavelengths from the space division switch 231 undergo a wavelength-band conversion through multiplexers 234 and 235, and the processed wavelengths are provided to the BXC switch 220. The space division switch 231 performs cross-connect switching between input/output wavelengths.
Although the above described switch system has a structure with a switching function according to multi-granularity, only the FXC switch that corresponds to the lowest layer is directly connected to the optical transport network so that the structure can be considered as basically a structure that one-dimensionally utilizes wavelength resources. Nevertheless, thanks to the switching function according to the multi-granularity, when traffic is aggregated by a waveband or by an optical fiber on the basis of WDM, switching can be performed on an aggregated unit basis without demultiplexing all the multiplexed waves. Accordingly, this structure is advantageous in that the space switching fabric of the optical cross-connect switching system can be simplified. That is, as the number of waves to be cross connected is increased, the optical cross-connect switching system is further simplified in proportion to the increased number of waves. However, wavelength resources included in the optical transport network are still used one-dimensionally so that the above structure does not contribute to such effectiveness of the network structure through the three-dimensional use of the wavelength resources as to be addressed shortly. In addition, the above structure does not satisfy the following preconditions that may be required for a three-dimensional use of the wavelength resources in order to form a more effective optical transport network in aspects of transmission of optical signals as well as topological simplicity.
The above-described preconditions may be summarized as follows:
First, the optical cross-connect switching system should have modularity so that the addition and subtraction of the FXC, BXC and WXC switching functions can be easily achieved, whenever needed, according to a position where the system is provisioned.
Second, the number of links, which are inserted or extracted at each layer of the FXC, BXC or WXC switch should be able to be easily rearranged.
Third, each layer of the FXC, BXC or WXC switch should be able to be independently connected to the optical transport network.
Fourth, the internal configuration change of the OXC switching system due to, e.g., number of insertion/extraction of links for interfacing local networks should not affect the optical transport network to which the corresponding OXC switching is connected.
Fifth, the OXC switching system should be easily adapted to the configuration change (that is, a change in the number of links connecting the network) of the network.
The structural disadvantages of the existing OXC switching systems have provided a motive for the present invention. In more detail, the insertion/extraction ports C1, C2 and C3/D1, D2 and D3 are physically fixed in FIG. 2, so the input/output ports of each space division switch should be manually changed when the ports are changed. Further, the number of the insertion/extraction ports and the number of the input/output ports A, B are mutually dependent, so the change of the extraction/insertion ports immediately affects the input/output ports, which in turn influence the network configuration. In more detail, the FXC, BXC and WXC switches are mutually and physically connected to one another, so there is difficulty in splitting or coupling and, upon splitting or coupling, the connection structure causes the change of related ports C and D, so the input/output ports or the network configuration are affected as mentioned above.
Meanwhile, for one of prior art optical cross-connect switching systems, “Optical wavelength space cross-connect switch architecture” has been registered as European Patent EP-1076469A2 on Feb. 14, 2001.
The switch architecture of the preceding patent is comprised of a plurality of Wavelength-Selection type optical Cross-Connect (WSXC) switch fabrics, which receive multi-wavelength input signals split by one or more wavelength splitters and produce wavelength-multiplexed output signals to be multiplexed by a plurality of optical couplers. The WSXC switch employs a Fiber Bragg Grating (FBG) as a wavelength selection element. By using this structure, the number of wavelength-multiplexed channels to be processed by each WSXC switch is reduced in comparison with the number of channels included in input signals that have been wavelength-multiplexed. In addition, a wavelength interval between adjacent channels to be processed by each WSXC switch becomes wider than an interval between adjacent channels in the wavelength-multiplexed input signals. Accordingly, the architecture of the prior patent can considerably reduce the number of wavelength-selective elements required to form an arbitrary path of the optical cross-connect switch.
However, the prior patent suggests the switch architecture considering only the cross connect of the optical wavelength unit, but does not suggest an architecture for three-dimensionally switching wavelength resources such as wavelengths, wavebands and optical fibers.